Periderm cells are cork cells in the stems of dicots. The periderm is produced by the phellogen ( cork cambium) toward the outside of the stem. The periderm contains suberin, a waxy substance, that seals the stem against water loss and invasion by insects, and infection by bacteria and fungal spores. There are typically 4-6 layer of periderm cells. DIAGRAM: Growth of Woody Stem PHOTO